I. Field of the Invention
The present invention relates to a system for pneumatically transporting powdered or granular materials, more particularly to an improved system for pneumatically transporting powdered or granular materials stored in an airtight storage container to a collector through a transport pipe in high density and at low speed by supplying pressurized gas.
II. Prior Art
FIG. 10 shows a conventional pneumatic transport system for use in powdered or granular materials. The system is constructed such that powdered or granular materials stored in an airtight storage container 100 are fed from the container 100 to a lower pipe 102a of a transport pipe 102 by the gas supplied from a gas feed pipe 101, then the materials are formed into a a plug 105 by supplying pressurized gas intermittently from a pressure nozzle 103 disposed intermediate of the lower pipe 102a, and then pneumatically transported in an upper pipe 102c of the transport pipe 102 through an inclined pipe 102b, and finally received in a collector 104.
However, when powdered or granular materials are pneumatically transported in the form of a plug as described above, the clearance 106 between the surface of the plug 105 and the inner surface of transport pipe 102 is often generated as shown in FIG. 11. As a result, only powdered or granular materials A on the surface of the plug 105 are transferred at first and the shape of the plug 105 is broken, thus the transportation cannot be done satisfactorily. Furthermore, since the conventional transport system delivers the plug 105 at extremely high speed like several meters per second for example, the materials are subject to strong impact when being caught in the collector 104, and the collision of materials frequently occurs. Accordingly, there is a problem of high possibility of defective products having chipping or breakage when fragile materials such as medical tablets are pneumatically transported.
A method and the related system for pneumatically transporting powdered or granular materials without giving an impact thereon and at extremely low speed was disclosed in Japanese Patent Application No. 61-251173(1986) to solve above mentioned problems.
FIG. 5 shows a basic structure of the transport system according to the above mentioned application, wherein a transport pipe 5 being disposed between an airtight storage container 3 and a collector 6 comprises a lower horizontal pipe 5a having a convergent cylindrical accelerating reducer 71 connected to the airtight storage container 3, an upper horizontal pipe 5c being connected to the collector 6 and having a divergent cylindrical decelerating reducer 74 at its initial end, and a riser pipe 5b which connects the pipes 5a and 5c and has a pair of reducers consisted of an upper convergent cylindrical accelerating reducer 73 and a lower divergent cylindrical decelerating reducer 72 intermediately thereof.
According to such a pneumatic transport system, tablets delivered from a tablet molding machine 2 to a vibration feeder 1 fall into the container 3 passing through a hopper 31 and an opened valve 32. The tablets are transported from the container 3 to the lower horizontal pipe 5a by the use of pressurized gas supplied from a gas feed pipe 4, and immediately thereafter continuously transferred upwardly into the vertical riser pipe 5b being charged into a high density to a degree just before blocking the lower pipe 5a by the accelerating reducer 71. While transferring upwardly, the tablets are once decelerated by the reducer 72 being disposed midway of the vertical pipe 5b, and again accelerated by the reducer 73 while keeping the materials being charged at high density to obtain sufficient pushing force, subsequently transferred upwardly into the upper pipe 5c.
Immediately after the tablets are moved up to the upper horizontal pipe 5c and shifted the direction into a horizontal direction, they are once more decelerated by the reducer 74 being provided at the initial end of the upper pipe 5c. As a result, the tablets are formed into a long column P as shown in FIG. 6 to enable to be pneumatically transported at very low speed without producing any clearance between the upper pipe 5c. Therefore, unlike the conventional system, the tablets on the surface of the long column P are not transported at first to cause the breakage of the column P. Moreover, it is prevented that the tablets are broken by colliding with each other while transporting in the upper pipe 5c.
The column P is formed longer corresponding to the length of the upper pipe 5c. The experiment of the invention showed that a column length L was more than 1 (one) meter when the upper pipe 5c was 5 (five) meters long and a column length was more than 3 (three) meters when the pipe 5c was 20 (twenty) meters long. And it also showed that the speed of transportation could be reduced to about 0.1 meter per second. Therefore, the tablets which are transferred at low speed in the form of column in the upper pipe 5c are further decelerated by a large-caliber elbow 8 being disposed at the terminal end of the pipe 5c and received in the collector 6 under substantial gravitational fall, thus complete the pneumatic transport.
As the tablets are pneumatically transported at low speed and finally collected under substantial gravitational fall, they are virtually free from damage. Therefore, the previous invention has been an epoch-making one to enable to transport the materials at high density without cracking or breaking when transporting compression moldings such as confectionery and electric parts and powders or granules and other solids as well as tablets.
However, after further researches on the invention, it was found that according to the pneumatic transport system, it was necessary to control the pressure of transport gas when the tablets were different in grain sizes, the control operation was troublesome, and the tablets would not be formed into a long column uniformly without controlling sufficiently.